报告题目：Premixed Flame Acceleration and Deflagration-to-detonation Transition
报告人：Damir Valiev（Tsinghua University）
Damir Valiev obtained his PhD from the Royal Institute of Technology (KTH), Sweden, in 2008. Subsequently, he held postdoc positions at Umeå University, Sweden, and at Princeton University, USA, also working as a long-term visitor at Sandia National Laboratories, Livermore, USA. Since 2014 he works as a senior research engineer at the Department of Applied Physics and Electronics, Umeå University, Sweden. In 2016, he joins the Center for Combustion Energy and the Department of Thermal Engineering at Tsinghua University, as an associate professor. He is a recipient of Thousand Young Talents Plan award. He has published more than 20 papers in peer-reviewed journals, including Combustion and Flame, J Fluid Mech, Phys Rev Lett, Phys Rev E. His research interests include modelling and numerical simulation of combustion, high performance computing, dynamics of premixed flames, deflagration-to-detonation transition.
In the present talk we will consider certain aspects of flame acceleration, subsonic and supersonic combustion in channels, and deflagration-to-detonation transition (DDT). At certain conditions a slow flame may spontaneously accelerate to near-sonic or supersonic speed and trigger detonation; this process is called DDT. In spite of extreme fundamental and technological importance, spontaneous flame acceleration and DDT remained, probably, one of the least understood processes in combustion science for about 70 years.
The first qualitative explanation of DDT was provided by Shelkin in 1940-ies. In the Shelkin scenario of DDT, a slow flame spontaneously accelerates to sonic velocities, pushes strong shocks heating the fuel mixture ahead of the flame front, which explodes and triggers detonation. It was a general belief that turbulence is a vitally important component of the DDT. Still, up to now turbulence remains one of the most difficult problems of modern physics, which was the fatal obstacle for quantitative understanding and predicting the DDT.
Only recently, a constructive idea was suggested that turbulence plays only a supplementary role in the acceleration. Starting with this idea, several groups of researchers developed the quantitative theory and performed simulations of laminar flame acceleration and DDT in smooth tubes. It was found that the flame accelerates in an exponential regime at the initial quasi-incompressible stage of the process. Later, experiments on DDT in micro-channels with diameter about 1 mm were performed, which demonstrated DDT in micro-channels in agreement with the theory. The current advances in understanding of DDT may open new technological possibilities for using DDT in micro-scale combustion energy devices, which is a rapidly growing area of research and development nowadays. DDT also stands behind many disasters like mining accidents and explosions in power plants: reducing the risk of unwanted DDT is a goal of primary importance for energy safety.